The present invention is related to a pneumatic tool, and more particularly to an improved continuously shooting pneumatic grease gun structure.
U.S. Pat. No. 5,779,105 discloses a continuously shooting pneumatic grease gun. The piston in the air chamber for driving grease push rod is formed with several escape holes. A corresponding valve rod is fitted in each escape hole for blocking the same. A spring exerts resilient force onto the valve rod, whereby when the valve rod is not under external force, the escape hole is kept free. Accordingly, when external high pressure air gets into the air chamber to drive the piston, the valve rod suffers the pressure to axially move to a position where the valve rod blocks a corresponding escape hole. At this time, the piston forwards and drives the grease push rod to push the grease out of the grease gun. When the forwarding operation of the piston is completed, the valve rods suffer a reaction force and are pushed away to unblock the escape holes. At this time, the high pressure air in the air chamber escapes out through the escape holes. Then the piston is restored to its home position by the spring for next reciprocation and successive shot.
According to the above structure, when the high pressure air in the air chamber escapes, the external high pressure air source still continuously fill high pressure into the air chamber. The successively filled in high pressure air immediately escapes through the escape holes without affecting the backward travel of the piston and hindering the piston from restoring to its home position. However, the resource of the high pressure air is wasted.